Bamboo is one of the most universally useful plant commodities known. Bamboo provides food, raw material, shelter and even medicine for the greater part of the world's population. However, information concerning the basic biology and reproduction of this complex and diverse group of plants lags behind that of other major agonomic plant species. Even the name bamboo is itself a vernacular term for more than 75 genera and 1250 species of the Gramineae (Soderstrom and Ellis, 1988 Smithsonian contribution No. 77), which are confused taxonomically as a result of their unusual flowering habits.
Once considered to be an inexhaustible source of raw material, bamboo is now threatened over a large area of the world. The "gregarious" flowering habit of bamboo, and the human population pressure disrupting the natural cycle of reforestation present an urgent need for the development of methods for large scale propagation of bamboo. Widely adaptable and efficient methods for vegetative propagation of bamboo on a commercial scale are not presently available. Bamboo could become an important new multipurpose tree crop in many areas where it has not been traditionally used, if reliable means of mass propagation were available. Another incentive for developing efficient mass propagation methods for bamboo is the increasing economic potential and aesthetic value of ornamental bamboos and grasses in the garden landscape (Reinhardt et al., 1989, Ornamental Grass Gardening; Friedman, N4 ).
Efficient in vitro propagation could prove to be a reliable and useful method for establishment of new bamboo plantations (Rao, et al. 1985, Plant Cell Report, 4:191-194). Rao, et al. demonstrated that it is possible to obtain somatic embryos from calli derived from cultured seeds of the bamboo, Dendrocalamus strictus. Only about 67% of the callus cultures formed well differentiated somatic embryos.
Similarly, Woods, et al. have accomplished somatic embryogenis in vitro from seeds of Mexican Weeping Bamboo (Woods, S., Phillips, G., Woods, J. and Collins, G., unpublished data). The efficiency of bamboo somatic embryogenesis was at least three times as efficient as that previously reported by Rao, et al., supra.
However, because bamboo rarely flowers and then flowers late in its life cycle there is a paucity of seed stores for bamboo. Thus, the establishment of parasexual alternatives to the use of seeds is necessary.
Somatic embryogenesis is now recognized as an acceptable method for plant propagation in vitro because it enables the rapid production of a large number of uniform plants within a relatively short period of time (Rao, et al., supra). The aseptic nature of regenerants formed in vitro is also useful in quarantine situations because such materials can be utilized for safe introduction of crops from one state or country to another.
The majority of research to date has been aimed at the development of shoot multiplication systems (Banik, R. L., 1987, in Rao, AN, et al. (eds), Proc. Internat. Bamboo Workshop, Hangzhov, 160-169; Manzur, MD., 1988, Agronomia 2: 14-19; Nadgauda, et al., 1990, Nature, 344: 335-336; Nadgir, et al., 1984, Silvae Genetica, 33: 219-223; Saxena, 1990, Plant Cell Reports, 9: 431-434. Plant regeneration via organogenesis from shoot apices was successful for four species (Huang, et al., 1989, Envir. Exp. Bot., 29: 307-315). There are only a few critical reports which deal with important economic bamboo species that provide significant contributions toward developing efficient protocols for somatic embryogenesis and plant regeneration. These include two reports of plants regenerated from floral structure explants (Yeh and Chang, 1986, Plant Cell Reports, 15:409-411; Yeh and Chang, 1986, Theor. App. Genet, 73: 161-163), and three reports of somatic embryogenesis and plant regeneration from seed explants (Yeh and Chang, 1987, Plant Sci., 51: 93-96; Mehta, et al. 1982, Proc 5th Internat. Cong. Plant Tissue Cell Culture, Fujiwara, Tokyo, 109-110; Rao, et al. 1985, supra). However, only one of these reports (Rao, et al., 1985) indicates potential as an efficient somatic embryogenesis system. A report of embryogenesis and plantlet regeneration from vegetative structures of green bamboo, Phyllostachys viridis (Hassan and Debergh, 1987, Plant Cell Tissue Organ Culture 10: 73-77), was followed later by a corrigendum indicating that the plant identified as green bamboo was incorrectly identified and was actually Pogonatherum paniceum (Lam) Hack., a grass (Hassan and Debergh, 1988, Plant Cell Tissue Organ Culture, 15: 93). Haploid plants obtained by androgenesis were reported recently for a bamboo species (Tsay, et al., 1990, Plant Cell Reports, 9: 349-351). Callus derived from vegetative structures was reported (Deckers, et al. In: Rao AN, et al. (eds) Proc. Internat. Bamboo Workshop, Hangzhou, 170-174; Huang, LC and Murasig T., 1982, Bot. Bull. Academia Sinica, 24: 31-52). Cell suspension and protoplast cultures have been investigated (Huang, et al., 1988, Bot. Bull. Academia Sinica, 29: 177-182; Huang, et al., 1989, Bot. Bull Academia Sinica, 30: 49-57).
Tissue culture of plants has primarily been concentrated on mature plant tissues for explants. Cells from mature tissues of some plants can be induced to multiply indefinitely in in vitro systems, to release free cells and small clumps of cells, and to produce somatic embryos from which normal plantlets can be generated. This concept recognizes that living mature plant cells are totipotent in that they retain in their nuclei the full genetic information of the zygotic nucleus and that the surrounding cytoplasm is capable of effectively carrying out the instructions from this genetic material. To date there have been no reports of successful culture and plant regeneration via somatic embryogenesis utilizing vegetative explants from mature bamboo plant parts. Such a means of mass propagation would make it possible to generate a large stock of uniform plants of selected bamboo species without the necessity of seeds.